Condition monitoring in electrical drives is usually obtained by means of external devices, i.e. hardware modules. These devices are installed in the plant along with the frequency converter, performing the analysis of the installation with their own sensors and software algorithms.
In some cases, the plant system is connected to a storage device where the important data are gathered for e.g. further post-processing and trending. These operations are usually performed non-real-time and in a passive manner in offline analysis on a separate computer, by exploiting time or frequency or time-frequency analysis of the data.
WO2011114006 A1 discloses a method for condition monitoring of electric and mechanical drives. The measurement data in the condition monitoring system of electric drives is collected at least from one electric drive. The measurement data is pre-treated and a frequency spectrum is created from the pre-treated measurement data with the Fast Fourier Transform and the detected vibration frequency and vibration amplitude are recorded from the frequency spectrum. The detected vibration frequency and vibration amplitude are compared to at least one detected vibration frequency and vibration amplitude successive in time. In the comparison, detrimental changes in vibration frequency and vibration amplitude are defined, and the detrimental changes are indicated.
The practice of offline condition monitoring does not allow a quick response to undesired conditions compared to a real-time-based monitoring system. This is due to the amount of time required to process the data, and the periodicity involved in the data acquisition process.
U.S. Pat. No. 6,507,789 discloses a gear transmission monitoring method. The method includes forming a good operating condition baseline matrix by, for each of a plurality of different gear mesh frequencies, obtaining a good operating condition signal indicative of gear transmission conditions over a segment of time and transforming the obtained good operating condition signal into a good operating condition time-frequency spectrum; and then obtaining a gear mesh frequency and a test signal over a segment of time, transforming the obtained test signal into a test time-frequency spectrum, and using the gear mesh frequency and the good operating condition baseline matrix to examine the test time-frequency spectrum to monitor gear transmission conditions.